IE71163B1

IE71163B1 - Acceleration sensor

Info

Publication number: IE71163B1
Application number: IE418590A
Authority: IE
Inventors: Gernot Hilger; Mechtilde Schmid; Hartmut Schultze
Original assignee: Mannesmann Kienzle Gmbh
Priority date: 1989-11-21
Filing date: 1990-11-20
Publication date: 1997-01-29
Also published as: PT95936B; EP0428952A1; PT95936A; EP0428952B1; DE59009091D1; ATE122792T1; JPH0645897Y2; IE904185A1; DE3938601A1; JPH0488862U

Abstract

Proposed for an accelerometer having a spring-mass system and a measuring transducer and consisting of a strip of amorphous metal and a coil arrangement assigned thereto is a design which has a high transverse stability, allows the overall space to be greatly compressed and, if required, enables machine assembly and rapid adjustment in conjunction with good reproducibility in mass production. In detail, apart from a screen (90, 91) assigned to the accelerometer (50) there are assigned to a seismic mass (81, 82), to which one end of the strip (68) is attached, two diaphragm springs (56, 59) which are supported by a supporting sleeve (51). It is possible to attach, by means of hot upsetting, to the latter at the face at one end a base part (58), and at the other end a carrier (60) for the coil arrangement (62) and the bearing for a winding mandrel (70), which serves for fastening the other end of the strip (68), as well as a cover (61), which exercises a braking function for the winding mandrel (70) and is provided with a socket (75). <IMAGE>

Description

The invention relates to an acceleration sensor with a spring-mass assembly, a coil arrangement and a measuring element in the form of a band of amorphous magnetoelastic metal, one end of the measuring element, which is electromagnetically connected to the coil arrangement, being connected to the mass and the other end being connected to a component of the acceleration sensor which is fixed with respect to the coil arrangement, and the mass, which has a central aperture larger than the external contours of the coil arrangement, at least partially surrounding the coil arrangement.

Acceleration sensors and force sensors of this kind which operate according to the magneto-elastic principle are particularly suitable for use in a severe medium, for example in a motor vehicle, because the measuring element itself, the measuring element in the form of a band and made from amorphous metal, referred to in the following text as a band, is distinguished by particularly good corrosion resistance and resistance to load variation, the measuring system formed by the band is highly sensitive and it is usually a simple matter to adjust an acceleration sensor that is fitted with it. Matching of the amorphous metal band specially to acceleration sensors is additionally provided for in that an extremely thin band, 20 to 30 pm thick and therefore extremely low in weight, can be manufactured, and this gives the acceleration sensor particularly outstanding directivity. This property is a particular advantage for use in motor vehicles where there is a high level of mechanical interference.

If acceleration sensors are to be used in a motor vehicle to capture accident data or to trigger driver information concerning running faults or dangerous driving situations, a plurality of acceleration sensors is required for the unambiguous, objective recognition of such driving situations, and these for example determine accelerations in the lengthwise, transverse and vertical axes of the vehicle, and this means that, as elements of a data-capture system, acceleration sensors of this type have to be able to be manufactured cost-effectively in spite of high precision, i.e. their manufacture must meet the conditions of mass production, and this means the simplest possible components and, where possible, the ability to be assembled by machines.

An acceleration sensor according to the generic type of Claim 1 has been made known with DE-U 89 09 652, in which the coil is located in a cylindrical sleeve and the movable mass is mounted on the sleeve by means of interposed ball bearings. The nature of the bearing in particular leads to highly complex assembly and does not permit assembly to be by machines.

Furthermore, DS-A 2 870 422 discloses an acceleration sensor which, apart from the fact that the measuring element is made up of layers of sheeting, has a number of components and requires a great deal of space, in addition, the construction of this acceleration sensor makes it unsuitable for mass production.

The object of the present invention was to create a design for an acceleration sensor in which the advantages of the measuring element in the form of a band are exploited to the maximum, sensitivity to the effect of transverse forces is largely reduced, and mass production is permitted.

The object is achieved in that the spring-mass assembly has two membrane springs which are fixed to the mass parallel to each other and on which the mass is suspended so that it can move with respect to the coil arrangement, in that a supporting sleeve equal in length to the mutual distance between the membrane springs and having an outer diameter equal to the diameter of the membrane springs is associated with the membrane springs, and in that a support which can be connected to the supporting sleeve is provided and on this are constructed means of freely bearing and accepting the coil arrangement and of fastening the one end of the band.

The achievement of the object provides a construction which is In particular optimised for the use of a measuring element in the form of a band and support which avoids the effect of tilting moments and has high transverse stability.

Furthermore, it is advantageous that the essential components of the acceleration sensor can be fitted in one direction, as it were, there being automatic centring and alignment with respect to the fastening points of the band and the relatively narrow space in the coil arrangement within which the band must lie without making contact. The structural type of the acceleration sensor according to the invention also possesses good reproducibility and enables assembly to be automated, i.e.- no fastening elements exlusively associated with the coil arrangement and/or the spring-mass assembly are used, the number of components is considerably reduced and components of complicated construction are avoided. Furthermore, the components are designed so that wherever possible -they can engage with each other and It is unnecessary to add tolerance, for example by using a support with which the spring-mass assembly, the coll arrangement and means of fastening the one end of the band are associated.

A particularly advantageous structural form is the coaxial location of coil arrangement and spring-mass assembly, which enables the overall dimensions to be reduced to the greatest possible extent and thus brings down the height of the structure. In this structural form the supporting sleeve Is both a bearing component and a reference component to which the other assemblies and components are fastened independently of each other and in this way the fitting tolerances are kept as low as possible.

It is, furthermore, of advantage that in this structural form only one connecting technique, namely hot-heading or welding, is used for connecting the individual components and assemblies to each other and for fixing the winding spindle, which when fitted is initially free to rotate.

In addition, the invention has the advantage that the acceleration sensor can still be adjusted mechanically, by measuring travel, after the base has been secured, in that the winding spindle is still freely accessible at this stage of assembly and the position of the springmass assembly can be determined on the other side by means of a suitable probe through a hole located in the base.

An acceleration sensor according to the inventions is described in greater detail in the following text, with reference to the attached drawings, in the drawingss FIGURE 1 shows a longitudinal section of the acceleration sensor, FIGURE 2 shows a partly cut-away front view of the acceleration sensor in the direction of the arrow in FIGURE 1, FIGURE 3 shows a view of a membrane spring from the spring-mass assembly.

FIGURE 4 shows views of individual components and assemblies of the acceleration sensor according to FIGURES 1 and 2, associated with one another in the manner ready for assembly.

As FIGURE 1 shows, the acceleration sensor 50 has a supporting sleeve 51, on each of the end faces of which a plurality of pegs, 52, 53, 54, 55 are directly moulded.

A first set of pegs, two of which, 52 and 53, are shown in FIGURE 1, serves on the one hand to mount the one membrane spring 56 of the spring-mass assembly 57 and on the other hand to secure a base 58, in that rivet heads are formed integrally on the pegs 52 and 53 which pass through the base 58, by hot-heading.

A second set of pegs, not all the same distance apart, one of which is identified as 54, and a third set of pegs formed integrally on the same face of the supporting sleeve 51, one of which is shown to represent the others and is identified as 55, serve on the one hand to mount the other membrane spring 59 and on the other hand to associate, without play, the spring-mass assembly 57 with a support 60 and secure it thereto, and to secure a cover 61 which is associated with the support 60, also by hotheading as already described.

In this embodiment the shape of the support 60 is such that the spring-mass assembly 57 and the coil assembly 62 can be located coaxially, with a particularly low overall height. This means that a shoulder 63 is constructed with a locating peg 64 on which a flat coil 65, which can comprise one or more windings depending on the measured values intended to be processed, is directly moulded on and free to move.

The coil arrangement 62 is at the same time constructed with a relatively narrow air gap 66 which is flush with a gap 67 located in the support 60 and provides frictionless passage for a band 68 which acts as the measuring element, in this embodiment the width of the gap 67 being in the order of 5 mm and the particularly critical dimension, namely the height of the gap, being in the lower range of tenths of millimetres.

A bearing shell 69 is also moulded onto the support 60 for a winding spindle 70 which takes up the one end of the band. In addition a plurality of contact elements which are associated with the flat coil 65 are embedded in the support 60, and of these one is identified as 71. Tongues 72 constructed on the contact elements 71 are used to secure the ends of the winding wires 73, while pins 74 which are also constructed on the contact elements 71 are associated with a plug, not shown, which is to be attached to the acceleration sensor from outside. The socket for the plug is moulded in the cover 61 and is identified as 75. The guiding and retaining function of the socket 75 is reinforced by tongues 76 and 77 (FIGURE 2), also constructed directly on the cover 61, and a sprung catch 78. A bearing shell 79 associated with the bearing shell 69 also forms part of the cover 61. The dimensions between the winding spindle 70 and the bearing shell 69 are chosen so that when the cover 61 is connected to the supporting sleeve 51 and the support 60, which is aided by a peg 80 constructed on the support 60, the winding spindle 70 becomes firmly clamped and an effect of friction for tensioning the band 68 is thus achieved by turning the winding spindle 70.

As already described, the membrane springs 56 and 59 are located parallel to each other and held in place at their outer edge by the pegs 52, 53 and 54, 55 constructed on the ends of the supporting sleeve 51. A bracket 81 which is connected to both membrane springs 56 and 59 serves to accommodate on the one hand the seismic mass 82 and on the other hand a winding element 83 associated with the other end of the band. This winding element 83 has a cylindrical section 84 and front cheeks, one of which is identified as 85 in FIGURE 1. To secure the winding element 83 a fitting guide 86 is constructed in the bracket 81 and the winding element 83 is secured in the guide 86 by the effect of the tension on the band 68. 87 identifies a sprung retaining means which acts on the coiled band, which is wound up in a number of layers on the cylindrical section 84 of the winding element 83, after the winding element 83 has been inserted in the bracket 81 and thus prevents the coiled band from springing out.

As can further be seen from FIGURE 1, the bracket 81 is provided with a central opening 88 which enables the spring-mass assembly 57 and the coll arrangement 62 to be located coaxially.

It should-also be mentioned that the cylindrical section 84 of the winding element 83 and a cylindrical section 89 of the winding spindle 70 are constructed in two parts.

In each case the two parts are joined together by means of a film .hinge and on the mutually facing surfaces there are constructed notched teeth, not given individual numbers, to ensure that the ends of the band are securely held. A domed housing, identified as 90, made from a magnetically highly conductive metal. Mumetal for example, provides magnetic screening. The domed housing 90 is flanged to the base 58, with a plate 91 which is also manufactured from magnetically highly conductive material being interposed, and the domed housing 90 has an aperture 92 giving access to the plug socket 75.

The cut-away section of the acceleration sensor 50 as shown in FIGURE 2 gives partial front views of the domed housing 90, the cover 61, the support 60 with the winding spindle 70 located In the bearing shell 69 and the membrane spring 59.

It can be seen from FIGURE 2 that the winding spindle 70 has cross slits 93 in the front so that it can be operated to tension the band 68. Access to each of the cross slits 93 is provided by an opening - in FIGURE 2 the one half of the opening constructed in the support 60 is identified as 94 - the diameter of the openings being mw»i im- than the diameter of the winding spindle 70. In this way the winding spindle 70, which is mounted in the bearing shells 69 and 79, is also secured axially.

FIGURE 3 is a view of the membrane spring 56. It has holes 95 in the outer circumference region which are associated with the pegs 52, 53 of the supporting sleeve 51. Slot-shaped openings 96, 97 are also provided, running circumferentially and offset with respect to each other. A central aperture identified as 98 is provided to enable the membrane spring 56 to fit onto a contour 99 constructed on the bracket 81 and corresponding to the aperture 98 (FIGURE 1). Holes 100 and 101, for fixing it to the bracket 81, are made, and these, together with pegs constructed on the bracket 81, enable the connection to be made by hot-heading. The membrane spring 59 is also secured to the bracket 81 in the same way, but because of the flat cross-section of the coil 65 the membrane spring 59, in addition to the holes spaced round the outer edge, has a differently shaped central aperture. It is clearly also conceivable that the slotshaped openings 96, 97 could be a different shape, e.g. arcuate. Furthermore, it is conceivable to design the membrane springs as point-symmetrically corrugated discs.

FIGURE 4 shows the conqponents and assemblies of the preferred acceleration sensor 50 mutually associated in the manner of assembly. Starting with the situation shown in FIGURE 4, the first stage of assembling the acceleration sensor 50 would preferably be to fit together the preassembled spring-mass assembly 57 and the assembly comprising the support 60 and the coil arrangement 62. The two assemblies can here only be positioned with respect to one another in one way because of the irregular pitch of the pegs 54, and this is critical for an unambiguous mutual alignment of the air gap 66 and the winding element 83. After this the free end of the band 68, which is wound onto the winding element 83, is threaded through the gap 66, 67 and the winding element 83 is inserted loosely into the guide 86 in the bracket 81 of the spring-mass assembly 57. The next step is to fasten the end of the band which protrudes from the support 60 to the winding spindle 70 and wind it up and to insert the winding spindle 70 into the bearing shell 69 provided in the support 60. The cover 61 is then placed on and fastened, and this cover 61 completes the bearing of the winding spindle 70 and the plug and socket connection. After this, in order to fasten the membrane spring 56 before applying tension to the band 68, the base 58 is flanged to the spring-mass assembly 57 and secured by hot-heading of the pegs 52, 53. During subsequent tensioning of the band 68 by turning the winding spindle 70 the membrane springs 56 and 59 undergo axial deformation. The required tensile force in the band 68 and thus the position of the working point of the acceleration sensor 50 is adjusted by measuring the electromagnetic properties of the coil arrangement 62 and the measuring element (band 68) and/or by mechanically scanning the position of the membrane spring 56, this being accessible through a suitable aperture in the base 58. After adjusting the pre-tension in the band 68, the winding spindle 70 and the cover 61, which acts as a brake during tensioning, are welded together, the sensor is introduced into the housing 90 and the housing is flanged to the plate 91 at the base 58.

The acceleration sensor 50 can be readily fastened to the chassis wall of a vehicle, for exanple, by adhesive bonding (the acceleration sensor 50 requires approximately 7 cm3), and can either be flanged on at the end face or inserted into a suitable aperture. It is also conceivable that by doing away with the plug socket 75 the acceleration sensor 50 can be directly arranged on a circuit board which carries the electronics needed to process the signals.

Claims

1. Acceleration sensor with a spring-mass assembly , a coil arrangement (62) and a measuring element (68) in the form of a band of amorphous magneto-elastic metal, one end of the measuring element (68), which is electromagnetically connected to the coil arrangement (62), being connected to the mass (81, 82) and the other end being connected to a component of the acceleration sensor (50) which is fixed with respect to the coil arrangement (62), and the mass (81, 82), which has a central aperture (88) larger than the external contours of the coil arrangement (62), at least partially surrounding the coil arrangement (62), characterised in that the spring-mass assembly has two membrane springs (56, 59) which are fixed to the mass (81, 82) parallel to each other and on which the mass (81, 82) is suspended so that it can move with respect to the coil arrangement (62), in that a supporting sleeve (51) equal in length to the mutual distance between the membrane springs (56, 59) and having an outer diameter equal to the diameter of the membrane springs (56, 59) is associated with the membrane springs (56, 59), and in that a support (60) which can be connected to the supporting sleeve (51) is provided and on this are constructed means (64) of freely bearing and accepting the coil arrangement (62) and of fastening the one end of the band (68).

2. Acceleration sensor according to Claim 1, characterised in that the membrane spring (e.g. 56) comprises a substantially flat disc in which slot-shaped openings (96, 97) are constructed.

3. Acceleration sensor according to Claim 1, characterised in that the membrane spring is constructed as a point-synnnetrically corrugated disc.

4. Acceleration sensor according to Claim 1, characterised in that the coil arrangement (62) has a locating peg (64) constructed on the support (60) and a coil (65) is moulded onto this peg (64).

5. Acceleration sensor according to Claim 1, characterised in that pegs (52, 53, 54, 55) are moulded onto the end face of the supporting sleeve (51) and in that openings associated with the pegs (52, 53, 54, 55) are provided in the membrane springs (56, 59), in the support (60) and in a base (58) which closes off the acceleration sensor (50) on the side opposite the support (60).

6. Acceleration sensor according to Claim 5, characterised in that the openings in the support (60) and the base (58) are constructed as through holes and in that the mutual connection of the spring-mass assembly , the support (60) and the base (58) is achieved by hot-heading the pegs (52, 53, 54, 55) which project through the through holes.

7. Acceleration sensor according to Claim 1, characterised in that a winding spindle (70) is provided for fastening the end of the band to the support (60), in that a first bearing shell (69) associated with the winding spindle (70) is formed on the support (60) and in that a cover (61) is provided which has a second bearing shell (79) and means for a fastening to a fixed component of the acceleration sensor (50).

8. Acceleration sensor according to Claim 7, characterised in that the support (60) end the cover (61) are connected to the supporting sleeve (51) on one and the same front surface of the supporting sleeve (51).

9. Acceleration sensor according to Claim 7, characterised in that a plug socket (75) is moulded in the cover (61)

10. Acceleration sensor according to Claim 1, characterised in that a domed housing (90) combined with a plate (91) on the front, the housing (90) being made out of a magnetically highly conductive material, is provided and is fastened to the base (58) of the acceleration sensor (50).

11. An acceleration sensor according to any one of the preceding claims substantially as herein described with reference to and as shown in the accompanying drawings.